The technical field of this invention is brake by wire system electrical architecture.
Brake by wire systems provide many advantages in brake system packaging and facilitate the expansion of new brake control features; but they also remove any direct mechanical or fluidic force transmitting path between the vehicle operator and the brake apply units. Thus, much thought is given to electrical failure modes and how to prevent loss of braking when such failure occurs. Two techniques useful in such systems are redundancy and fault monitoring. This invention combines each of these techniques in a brake by wire system electrical architecture.
The vehicle brake by wire system of this invention provides three electrical power sources. One of these is a first electric generator; another is a first electric power storage device; and the third may be either a second electric generator or a second electric power storage device. One or more brake units for wheels of a vehicle are connected for activation by one or more control units having electric power inputs.
An electric circuit has a common node and (1) connects the first electric generator to the common node through a first unidirectional current control device having a first forward voltage drop, (2) connects the first electric power storage device to the common node through a second unidirectional current device having a second forward voltage drop, (3) connects the electric power source to the common node through one of the first and second unidirectional current devices, and (4) connects the common node to the electric power inputs of control units through circuit breaker devices. A sub-circuit within the electric circuit interconnects the first and second unidirectional current devices, the common node and the first and second circuit breaker devices and isolates them within a zone protected from short circuits to points outside the zone and reduces the possibility of open circuits in the zone.
A control is provided for separately sensing a voltage across each of the first and second unidirectional current devices while controlling activation of the first electric generator and (if present) the second electric generator so as to reverse bias the other of the first and second unidirectional current devices. By interpreting the sensed voltages across the two diodes, an electrical short or open circuit may be detected in the electric circuit.